Constant speed motor



Feb. 27, 1940. suoncnoss 2,192,051

cous'rm'r srimn MOTOR 0x11111111 Filod Aug. 30, 1937 IF 7 l Xmas-21%Patented- Feb. 27, 1940 chiral) STATES CONSTANT SPEED MOTGR Austin 8..Noreross, Waban. Mass.

ilirlginal application August 30, 1937, Serial No. 361,614.. Divided andthis application July i4, 193%. .fieriai No. 284.508

4. Claims.

to a novel two of motor no commutation and power current commutatormotors. 3 invention are particularly ale-phase motor described in So.ZJMSGJOG, operating as a otor. This application is a co division Alt-errfrom synchronism the speed voltage changes so that the neutralizationbecomes less eflective and consequently the commutation becomescontinually poorer'ior higher or lower speeds. This factor usuallylimits the speed range that may be obtained from adjustable speedmotors.

utilizing the principles of my invention it is possible to have nearlycomplete neutralization of the transformer voltage by a speed voltage.Employing my invention, an alternating current commutator motor may beoperated as a constant speed motor having good commutation at a speeddiffering greatly from synchronism. Thus for example, by operating atwo-pole motor considerably above synchronous speed, a very high speedmotor may be obtained which has shunt speed characteristics and goodcommutation.

In order toxprovide desirable characteristics, particularly goodcommutation,I determined after much study that a motor constructed tooperate in accordance with two definite formulae, which will be setforth later, would provide these de-- 4 sirable characteristics. Thisapplication coversia constant speed motor to operate at a speeddiffering greatly from synchronism with the windings so arranged andconnected'so that they satisfy these two equations. 1

A further object of myinvention is not only to design a motor inaccordance with said equations which will operate with improved commutation characteristics, but also to provide in combination therewithmeans to provide in 'the rotor a power factor improving component ofvoltage as well as to improve thepower factor thereof. Inthesingle-phase motor shown in my former patent, it is apparent that thecapacitator itself provides means to provide in the rotor a 55 powerfactor improving component of voltage. I

non of my application for out commutator motor, Ser. No.

' (Cl. 197M276) employ a simiiar type of capacitator in my pl'resentinvention.

Further features of my invention relate to innprovements in the specificstructure for carrying out the principles thereof.

These and such other objects of my invention as may hereinafter appearmay be best understood from a description of the accompanying drawingwhich illustrates an embodiment thereof.

In the drawing, Fig. l is a circuit diagram of a constant speed motorconstructed in accordance with my invention.

Fi .vv 2 is a vector diagram showing approximately the phase relationsof the speed and transformer voltages induced into thecoils undergoingcommutation in the type of single-phase motor shown in Fig. 1.. x

In the drawing,,wherein like characters of reference generally indicatelike parts throughout, Figs. 1 and 2 illustrate an embodiment ofsingle-phase motor constructed in accordance with the principles of myinvention. 'I'he'single- In the structure shown in Fig. 2 of saidpatent,- I' have provided adjustable means to supply voltage to the mainstator winding and adjust- .winding. In the structure shown in saidpatent, however, the armature is permanently shortcircuited. In order toimprove the commutation throughout and to provide a greater speedran'ge,

I may so modify the' structure shown in my :former pat'entas toadjustably vary the voltage also supplied to the armature winding asshown in said parent application. Instead of short circuiting thearmature A, I may, as shown in said application, adjustably connect thearmature to the auto-transformer T shown in Fig. l thereof, or tothetransformer T shown in Fig. 2 thereof to receive an adjustablevoltage therefrom. In

able means to supply voltage to the quadrature 1 the type ofsingle-phase alternating current motors shown in Figs. 1 and 2, herein,I have the stator windings.

In the particular embodiment shown in Fig. 1 of said parent application,voltage is impressed from the main line 20 or source of supply onto theauto-transformer T, where in turn it is impressed upon the main windingM and the quad rature winding Q as shown in said patent. By

adjusting the positions of the riders MR. and, QR for the main windingand the quadrature winding on the auto-transformer shown in Fig. 1 ofsaid parent application or the single rider (M+Q)R on the transformershown in Fig. 2 of said parent application, the voltages impressed uponthe main and quadrature windings may be varied as shown in said patent.As also shown in said patent, I provide means toprovide in the rotor apower factor improving component of voltage comprising the capacitator Cconnected in the quadrature field circuit. As stated in said patent, thecapacitator C, in addition to improving the power factor, improves thetorque, commutation and other desirable characteristics of. the motor.

The armature A rotates within the stator and is provided with acommutator having brushes B. Instead, however, of short-circuiting thearmature as shown in said patent, I adjustably impress voltage upon thearmature winding from the transformer or auto-transformer T by means ofadjustably moving the supplemental rider AR relative to said transformeror auto-transformer. I have found in practice that by supplementallyadjustably impressing or varying the voltage impressed upon the armaturewinding, I am enabled to increase the speed range as in the embodimentsshown in said parent application and in general improve the operatingcharacteristics of the motor.

The speed of this motor may be adjusted by controlling m; and q asdescribed in the abovementioned patent, or by controlling the voltage VAimpressed upon the brushes. The voltage VA is substantially in phasewith Eur above synchronous speed and in phase opposition to it belowsynchronous speed. It will be observed by referring to Fig. 3 of theabove-mentioned patent that adding a voltage VA in phase with Emwillresult in an increase in Eqs and a corresponding increase in speed.Similarly adding a voltage VA in phase opposition to Eur will decreaseEqs and the speed. Inasmuch as VM and VQ vary in proportion to in and4n, the speed of this motor may therefore be adjusted by controlling anyone or all three of the variables Vu. Va and VA, and may beapproximately expressed by the following algebraic equation:

where Z is the impedance of the armature circuit and Is. equals thearmature current. This expression assumes that Eos is in phaseopposition to EMT which is substantially the case as Eqs is onlyslightly displaced from this position to improve the performance of themotor.

The resultant voltage induced into the coil undergoing commutation mustbe small to prevent brush sparking and excessive losses due tocirculating currents. This resultant voltage is made up of a transformervoltage es which is produced by the quadrature field flux and a speed.voltage es which is produced by the main field flux. In the case of thesingle-phase motor referred to, these two component voltages aresubstantially in phase opposition to each other as shown by Fig. 4 sothat the best commutation is obtained when e:=e. (2) where e=K f and6a==KI7L Therefore, in adjusting the speed of the abovementionedsingle-phase motor. shown in said parent application, in accordance withEquation 1, it is advisable to adjust the controlling factors 4m, e andVA in such a manner as to approximately satisfy Equation 2. Furthermore,it is possible to adjust the quantities 4m, m and VA in such a way as tosatisfy Equations 1 and 2 and at the same time maintain particularhorsepower or torque characteristics. For instance, by adjusting 4 qinversely proportional to the speed, the motor will be inherently aconstant horsepower motor, while if M is maintained constant the motorwill be inherently a constant torque motor.

In some cases it may not be practical to keep e; and e. exactly equalthroughout the entire speed range. For example, as shown in Fig. 5 ofsaid parent application, Vu, Va and VA are adjusted to satisfy Equation2 and maintain constant horse-power characteristics, only abovesynchronous speed. To maintain the same horsepower characteristics andkeep as equal to as below synchronous speed, excessive main andquadrature field fluxes would be required if the fleld fluxes werenormal at synchronous speed. Under this condition it might be advisableto obtain the speeds below synchronism by keeping Va and Vq constant andadjusting VA as indicated in Fig. 5 of said parent application. Whileeis not exactly-equal to es when this is done. the resultant voltageinduced into the coil undergoing commutation is small for speeds fromsynchronous to one-half synchronous speed. Constant torquecharacteristics will then be obtained below synchronous speed.

There are other cases where it may not be practical to maintain eexactlyequal to es throughout the speed range. For example, if

V: is kept equal to Vq as indicated in Fig. 6

of said parent application the auto-transformer is obviously simplifiedand the small difference between e. and et in this case will not produceappreciable brush sparking throughout a large speedrange.

The two component voltages er and e. will be exactly in phase oppositionwhen the two fields on and m are in exact time quadrature. In this casethe two oscillating fields are in both space and time quadrature andwhen they are equal a circular revolving field results which isidentical with that obtained from a polyphase machine. It thereforeshould be evident that commutation in a polyphase motor is equivalent tothat of a single-phase motor when the main and quadrature fields areequal and in time quadrature.

The conditions of Fig. 6 of said parent application therefore areapplicable to a polyphase motor where the voltages indicated arephasevoltages as shown in Fig. 13 of said parent application. By meansof a circuit arrangement, such as indicated in Fig. 11 of said parentapplication, the speed of a three-phase commutator motor may be adjustedby controlling the voltages impressed upon the stator and armature willbe apparent from an inspection of Figs. 1

and 5 of said parent application, there are three variables, namely, Vn,Va and VA- I have shown in Fig. 1 of said parent application riders MR,

QR, and AR. to adiustably contact the autotrans former '1". to provideindependent variation of each of these three variables. It is apparentthat if a voltage regulator be provided which will supply voltages toeach of the stator windings, including the main winding and quadraturewinding and the armature winding, separately and independently, in suchpredetermined combinations varying for diiferent speeds in accordancewith these curves or other curves to satisfy the respective equations atdifferent speeds, the speed andtransformer voltages induced into thecoils undergoing commutation will be substantially equal at all speeds.

It is also apparent that instead of providingadjustable riders as shownin said parent application to vary the voltages impressed upon thearmature, main and quadrature windings, either jointly or independently,said respective windings maybe arranged and connected to the supply insuch a predetermined combination as to cause the speed and transformervoltages induced into the coils undergoing commuta ion to besubstantially equal at any speed above or below synchronism. This may bedone by permanently fitting the adjustable riders against the desiredpoints in the desired predetermined combination of a transformer orauto-transformer, in accordance with the curves shown in Figs. 5 or 6 ofsaid parent application, or otherwise in accordance with said equations,or it may be done by varying the general design of the motor to cause itto operate in accordance with said equations. I have shown in Fig. 1 ofthis application a constant speed motor constructed in accordance withmy invention, with the desired number of turns in the respective main,quadrature, and armature windings to satisfy said equations.

It is preferable in designing this motor to design the quadraturewinding and the capacitator so that when they are directly connected tothe supply they will provide the desired quadrature field fiux. m. Themain winding and armature windings may then be designed to produce amain field fiux which will satisfy the Equations 1 and 2 when the mainwinding and the armature windings are connected directly to the supply.

It should be obvious that these principles are applicable in many otherforms for adjustable speed motors and are also useful for constant speedmotors. For example, a very high constant speed motor may be obtained byoperating a tWO-P le motor at a speed considerably greater thansynchronism. In such a case the transformer may be entirely eliminatedas in Fig. 1.

This motor is particularly suitable for high speeds greater than 3600 R.P. M.

It is thus apparent that Ihave provided a convoltage and trol for analternating currentmotor, which may be operated as a constant speedmotor to operate in accordance with the principles of my invention andwhich may, if desired,-be provided in combination therewith with meansto provide in the rotor a power factor improving component of having theadvantages explained above.

For convenience, I append a list of the symbols used in thisspecification in referring to the various electric forces considered.

M=Main field flux. =Quadrature field flux. Vs=Voltage impressed onbrushes. Eur=Transformer voltage induced into armature from main fieldflux. Eqs=Speed voltage generated in armature from quadrature fieldflux. l Vu=Main field voltage.

' Vq=Quadrature field voltage.

It is understood that my invention is not limited to the specificembodiment illustrated herein and that various deviations may be madetherefrom without departing from the spirit and scope of the appendedclaims. I

What, I claim is;

1. In combination an alternating current motor comprising'a mainwinding, a rotor having a coiled commutator armature winding, brushesplaced substantially along the axis of said main winding, a quadraturewinding spaced ninety electrical degrees from the main winding, and

dephasing means in the circuit of the said quadrature winding comprisinga capacitator of such magnitude as to dephase the circuit of thequadrature winding relative to the main winding by an amount to producean angle having a cosine between .5- and'l between the armature currentand the quadrature field flux, said windings being arranged andconnected to the supply in such a predetermined combination inaccordance with predetermined voltage and speed characteristics cosinebetween .5 and 1 between the armature current and the quadrature fieldflux, said windings being arranged and connected to the supply in such apredetermined combination in accordance with predetermined voltage andspeed characteristics as to cause the speed and transformer voltagesinduced into the coils undergoing commutation-to. be substantiallyequal.

-3. In combination, an alternating current motor comprising a mainwinding, a rotor having a coiled commutator armature winding, brushesplaced substantially along the axis of said main winding, 9. quadraturewinding spaced ninety electrical degrees from the main winding, anddephasing means in the circuit of the said quadrature winding comprisinga capacltator of such magnitude as to dephase the circuit of thequadrature winding relative to the main winding by an amount to producean angle having a cosine between .5 and 1 between the armature'currentand the quadrature field flux. said windings being arranged andconnected to the supply to provide voltages and fluxes substantially inaccordance with the equations e=e| and I.Z+ uf=l= 4 v M Y 4. Incombination, an alternating current m tor comprising a main winding,",arotor having a coiled commutator armature winding, brushes placedsubstantially along the aids of main winding, a quadrature windingspaced ninety electrical degrees from the main winding, and means fordephasing the current in said quadrature winding to produce an anglehaving a cosine between .5 and 1 between the armature current and thequadrature fleld flux, said windings being arranged and connected to thesupply to provide voltages and fluxes substantially in accordance withthe equations e:=e' and Ans-rm s. uoncnoss.

